1. Field of the Invention
The present invention relates to a finisher used while connected to an image forming apparatus such as a copying machine, printer or multifunction peripheral (MFP) and the method of sheet processing performed by such finisher.
2. Description of the Related Art
As a second sheet processing apparatus (finisher) that is used in combination with a first sheet processing apparatus such as a copying machine, an apparatus has been proposed that accumulates sheets after creating a fold line in the center of each sheet supplied from the first sheet processing apparatus, and binds the sheets in the center (center-binding) by placing staples along the fold line (see Japanese Laid-Open Patent Application No. H9-12211, for example).
In this second sheet processing apparatus, a fold line is created in the sheet by a sheet folding unit that is disposed in the conveyance path while the leading edge (the first edge) of the sheet introduced into the apparatus is held in place using a regulator plate, the conveyance of the sheet is then reversed (i.e., the sheet is ejected from the sheet folding unit with the trailing edge (the second edge) advancing first), and the sheet is conveyed along a reverse path and ejected onto a tray. Multiple sheets are accumulated in this way to create a packet of sheets. After the grouped sheets are aligned along the first edge using a regulator plate, the packet is conveyed to the stapling position, at which staples are driven into the fold line.
Incidentally, sheets vary in size. For example, landscape-oriented A4-size sheets (here, the length of the sheet is perpendicular to the direction of conveyance) have a length falling within the range of 210±2 mm. Therefore, where each sheet is folded using the first edge as a reference point, and stapling is carried out using the second edge as a reference point, for example, the staples may be offset slightly from the fold line. In contrast, using the construction of the conventional apparatus described above, because folding and stapling are both performed after the sheet or packet of sheets is positioned using the first edge as a reference point, staples can be accurately driven into the fold line even if the sheets vary in size.
In the conventional art, the second sheet processing apparatus is generally installed next to the first sheet processing apparatus, which comprises a copying machine or the like, but in recent years, a compact image processing system is proposed that is composed of a first sheet processing apparatus and a second sheet processing apparatus, wherein at least part of the second sheet processing apparatus is disposed within the first sheet processing apparatus such that the space that would have been required for installation of the second sheet processing apparatus may be eliminated.
However, where the second sheet processing apparatus has a binding mode such as a center-binding mode in which a fold line is created in sheets and staples are driven into the fold line, the system inevitably becomes large in size because, as described in Japanese Laid-Open Patent Application No. H9-12211, for example, a reverse path or the like must be included in order to use the same edge of the sheet or packet of sheets as the reference point for the folding and stapling operations in the manner described above.